mode-cfb.ts•2.37 kB
// Cipher Feedback
import { ModeOfOperation } from "./mode.js";
export class CFB extends ModeOfOperation {
#iv: Uint8Array;
#shiftRegister: Uint8Array;
readonly segmentSize!: number;
constructor(key: Uint8Array, iv?: Uint8Array, segmentSize: number = 8) {
super("CFB", key, CFB);
// This library currently only handles byte-aligned segmentSize
if (!Number.isInteger(segmentSize) || (segmentSize % 8)) {
throw new TypeError("invalid segmentSize");
}
Object.defineProperties(this, {
segmentSize: { enumerable: true, value: segmentSize }
});
if (iv) {
if (iv.length % 16) {
throw new TypeError("invalid iv size (must be 16 bytes)");
}
this.#iv = new Uint8Array(iv);
} else {
this.#iv = new Uint8Array(16);
}
this.#shiftRegister = this.iv;
}
get iv(): Uint8Array { return new Uint8Array(this.#iv); }
#shift(data: Uint8Array): void {
const segmentSize = this.segmentSize / 8;
// Shift the register
this.#shiftRegister.set(this.#shiftRegister.subarray(segmentSize));
this.#shiftRegister.set(data.subarray(0, segmentSize), 16 - segmentSize);
}
encrypt(plaintext: Uint8Array): Uint8Array {
if (8 * plaintext.length % this.segmentSize) {
throw new TypeError("invalid plaintext size (must be multiple of segmentSize bytes)");
}
const segmentSize = this.segmentSize / 8;
const ciphertext = new Uint8Array(plaintext);
for (let i = 0; i < ciphertext.length; i += segmentSize) {
const xorSegment = this.aes.encrypt(this.#shiftRegister);
for (let j = 0; j < segmentSize; j++) {
ciphertext[i + j] ^= xorSegment[j];
}
this.#shift(ciphertext.subarray(i));
}
return ciphertext;
}
decrypt(ciphertext: Uint8Array): Uint8Array {
if (8 * ciphertext.length % this.segmentSize) {
throw new TypeError("invalid ciphertext size (must be multiple of segmentSize bytes)");
}
const segmentSize = this.segmentSize / 8;
const plaintext = new Uint8Array(ciphertext);
for (let i = 0; i < plaintext.length; i += segmentSize) {
const xorSegment = this.aes.encrypt(this.#shiftRegister);
for (let j = 0; j < segmentSize; j++) {
plaintext[i + j] ^= xorSegment[j];
}
this.#shift(ciphertext.subarray(i));
}
return plaintext;
}
}